Disposable absorbent articles such as diapers and adult incontinence products are well known in the art. Such disposable articles collect and retain urine and fecal material deposited thereon by the wearer.
Nonwoven fabrics made of synthetic fibers and/or natural fibers are commonly used in absorbent articles, for example, as topsheet material or as core wrap to enclose the storage layer of the absorbent core. Such nonwoven fabrics are usually hydrophobic. However, for many applications in hygiene products it is necessary to have hydrophilic nonwoven. Therefore the nonwoven fabric has to be treated accordingly.
One typical component of disposable absorbent articles is topsheets. A topsheet is typically a nonwoven material designed to provide an interface between the wearer and the absorbent core of a disposable absorbent articles as well as providing the first point of contact for any bodily waste exuded by the wearer. They may be a film, or more typically they are a nonwoven material which has been rendered hydrophilic.
A common method for rendering nonwoven fabrics hydrophilic is coating the surface of the nonwoven with hydrophilic surfactants. As this coating does not lead to a tight chemical bond between the nonwoven and the surfactant, the surfactant can be washed off during use when the absorbent article is wetted. The decrease in liquid strike-through time is a desirable effect when the nonwoven is coated with surfactant. Liquid strike-through refers to liquid passing through the nonwoven fabric with liquid strike-through time referring to the time it takes for a certain amount of liquid to pass through the nonwoven. However, as the surfactant is washed off when coated nonwoven fabrics are exposed to the liquid, the strike-through time in the next gushes is increased. This results in performance reduction during use on diapers or other articles comprising such nonwoven fabrics. Furthermore, at the same time as liquid strike-through time decreases due to use of surfactants, surface tension of the liquid, which was in contact with the nonwoven fabric, is reduced. This reduction is undesirable, because it can cause increased urine leakage in a diaper.
Another common method to render a nonwoven fabric or films hydrophilic is by applying corona and/or plasma treatment. Plasma is an ionized form of gas that can be obtained by ionizing a gas or liquid medium. Plasmas are widely used for the treatment of organic and inorganic materials to promote adhesion between various materials. Polymers that have chemically inert surfaces with low surface energies do not allow good coatings with bondings and adhesives. Thus, these surfaces are treated to make them receptive to bonding with other substrates, coatings, adhesives and printing inks.
However, corona and plasma treatments lead to low coating durability upon storage of the treated material, i.e., hydrophilicity decreases over time.
Thus, there is a need for a hydrophilic coating of a nonwoven, which is durable upon storage, is not easily washed off when wetted and allows the nonwoven to achieve fast liquid strike-through in multiple exposures to liquid.
It should be understood that every limit given throughout this specification will include every lower or higher limit, as the case may be, as if such lower or higher limit was expressly written herein. Every range given throughout this specification will include every narrower range that falls within such broader range, as if such narrower ranges were all expressly written herein.